Microbial Cell Densities, Community Structures, and Growth in the Hydrothermal Plumes of Subduction Hydrothermal Systems

Abstract

In this report, we compile a study of microbial populations in deep-sea hydrothermal plumes with providing some new data set, and discuss the relationships with geological settings and the type of the hydrothermal system, e.g. ridge or subduction, in the context of the hypothesis “four TAIGAs” (Urabe et al. Chap. 1). Deep-sea hydrothermal plumes represent one of the best habitats for chemolithotrophic microbes to drive primary production in hydrothermal systems. Microbial cell densities in hydrothermal plumes are up to several times more elevated than in the general abyssal seawater. Putative sulfur utilizers, e.g. SUP05 and Alcanivorax in gammaproteobacteria, SAR324 in deltaproteobacteria, and several epsilonproteobacteria, are the dominant microbes that are detected from most of hydrothermal plumes. The microbial community compositions in the plume of an arc-backarc system are different from those of a mid-oceanic ridge hydrothermal system. This is because the cell densities and community composition of the putative sulfur oxidizers may be regulated by reduced sulfur species due to the pH and Eh conditions of the subseafloor and surrounding seawater. Aerobic methanotrophs are found in hydrothermal plumes which contain high concentrations of molecular hydrogen and methane. Quantitative microbial cell analysis by catalyzed reporter deposition based fluorescent in situ hybridization (CARD-FISH) show that the SUP05 populations are 60–100 % responsible for increased microbial cell densities in the hydrothermal plumes of arc-backarc fields. The contribution of the SUP05 cell densities in the plume microbial community is closely connected with the chemical energy from hydrothermal fluids in various types of TAIGA.